High-Speed Rail is one of important transportation tools in many countries, such as TVG in France, ICE (Inter-City Express) in German, Shinkansen in Japan, and Taiwan High Speed Rail. With the development of the high-speed rail and the popularity of the communication equipment, the demands of the network are rapidly increasing in fast moving scenarios. In general, a highest speed of a train in the High-Speed Rail is approximate to 280 kilometers per hour. Under such a high moving speed, the variation of the signal quality within a short time would be quite large. And, influenced by the Doppler Effects, the decoding error rate at the receiving side would increase. This makes the User Equipment (UE) frequently try to resend data when the network connection is interrupted. Generally, before an UE to access the Internet, the UE must accept an authentication, such as authenticated by an authentication authorization accounting (AAA) server. However, if an authentication process to authenticate the UE failed due to the network disconnection, the UE would continuously try to resend the authentication data to complete the authentication process.
FIG. 1 is a block diagram illustrating a network system of a train 100. The train 100 in FIG. 1 could be a train, a High-Speed Rail, or other transportation with a predictable traveling route and multi-cars. The rain 100 may include five cars 100_1˜100_5. In this embodiment, the access points (APs) 102_1˜102_5 could be disposed respectively to cars 100_1˜100_5 in the train, and could respectively provide the passengers in cars 100_1˜100_5 with network access capabilities. For example, the access point 102_1 could provide the passengers in 100_1 car to access the network with mobile devices (such as mobile phones, tablet PCs, notebook computers or other similar devices), and access point 102_2 could provide the passengers in car 100_2 network access, and the remaining access points 102_3˜102_5 likewise.
As shown in FIG. 1, the train 100 disposed only a single External Gateway 104 (for example, a client device (Customer Premise Equipment, CPE) gateway) connected to the car 100_3. Gateway 104 could be connected to APs 102_1˜102_5, and as an intermediate access point to communicate with the network 106 between cars 102_1˜102_5. Network 106 could be, but not limited to long-range evolution (LTE), WiMAX (worldwide interoperability for microwave access, WiMAX), third generation mobile communication networks (3Gs), the fourth generation of mobile communication networks (4Gs) or other similar networks. Although FIG. 1 is not explicitly depicted the configuration of network 106, but it is substantially based on communication standards and could be configured to include corresponding network entities. For example, if using the LTE network to communicate 106 and the gateway 104, network 106 may include an enhanced node B (eNB), a mobility management entity (MME), serving gateway (S-GW), and packet data network gateways (P-GW) and other network entities, but not limited thereto.
Since the train 100 has only a single External Gateway 104, so that the channel quality between the gateways 104 and the network 106 would be changed rapidly when the train 100 was moving, and the situation of network disconnection would occur often. When the authentication process of UE failed, the transmission queue of the external gateway would be filled with the authentication data, and it could cause network congestion.
In addition, even if an additional redundant Gateway was built in car 100_3 like gateway 104 to shunt the traffic of gateway 104, the overall transmission efficiency still could not reach the channel diverse effect because the channel quality of the redundant gateway is similar to that of the gateway 104.
In the network topology built by the well-known train, there is only one single configuration of an external (outbound) gateway. As previously mentioned, when the authentication process of an UE failed, the transmission queue of the external gateway will would be filled with the authentication data, and the phenomenon of network congestion could occurs.